The embodiments of the present invention relate to a forming die for shaping a workpiece, in particular a flat metal sheet, and to a method for arranging a temperature-control device on a forming die.
Forming apparatuses or forming dies which serve for example for the shaping of metal sheets in presses usually have a female part with a shaping surface and a male part, for example a punch, having a separate shaping surface that corresponds to the shaping surface of the female part. The metal sheet is introduced between the female part and the punch and formed by way of a relative movement of the punch in the direction of the female part or by way of a movement of the female part in the direction of the punch, wherein the metal sheet is clamped between the female part and the punch. In order to improve the forming result and in order to avoid bending up of the workpiece to be formed, i.e. the metal sheet, in the peripheral regions of the female part, holding-down means are used. These holding-down means, also known as blank holders, hold the metal sheet against the female part so that it cannot bend up. In addition, the holding-down means ensure continued flowing of the sheet material so that stress cracks are avoided.
The forming die has regions with lower degrees of forming and regions with higher degrees of forming. In regions with a high degree of forming, strong deformation of the workpiece, i.e. of the metal sheet, occurs. Tests have shown that the metal sheet can crack in these regions. This crack formation is attributable to the fact that, at a high workpiece frequency, or number of strokes, the die heats up in sections with high degrees of forming. As a result, high temperatures, which are above room temperature or exceed the temperature which the metal sheet exhibits prior to forming, are achieved in these sections. During the forming of a metal sheet, friction occurs between the metal sheet and the forming die, in particular in regions with high degrees of forming, with the result that the die heats up. This results in expansion of the die and thus to a change in shape. Depending on the friction and degree of forming, locally different expansions of the die occur. As a result, the available space for a subsequent metal sheet to be formed is reduced at these points, and so cracks can occur.
Such problems require reworking of the die. In this case, one or more segments of a forming die half are cut out, i.e. the female part or the male part. Inserts which are provided with a plurality of holes are then introduced into these cutouts. These holes are combined with one another such that a cooling circuit can be produced in an insert. In this case, a first hole is produced from an outer side of the die insert. Subsequently, a second hole is positioned such that it intersects the first hole inside the die insert. According to this method, a plurality of holes are introduced. Subsequently, openings on the surface of the die insert that are not required are closed off by plugs, apart from an inlet and an outlet. This results in a cooling circuit through which a medium can flow. Subsequently, the insert is inserted into the female part or the male part. However, this method has the disadvantage that the cast structure of the female part, the male part or the blank holding-down means is no longer cohesive, but consists of different individual parts (cast structure and insert). In particular when the female part is formed from a cast material, there is the risk that the female part will be destroyed during use as intended. The separation of a segment from the forming die made of cast material thus represents a weakening of the cast structure. If, for example, the punch now forms the workpiece and passes into the male part together with the metal sheet, it generates a pressure load on the female part, which can act in the radial direction and in the axial direction in the cavity. This pressure load can have the result that the die half having a weakened cast structure is destroyed.
As an alternative to the introduction of cooling ducts, it is possible to completely remake the die. In this case, it is also possible for new dies to be provided with inserts from the outset, wherein the cast structure of these inserts is optimized. However, this represents an extremely unsatisfactory solution economically.
an object of the embodiments of the present invention is to specify an alternative solution with which regions of a forming die which have a high degree of forming are temperature-controllable. An exemplary object of the embodiments of the invention is to specify a forming die and a method with which subsequent temperature control or cooling of critical regions of the forming die is realizable.
This and other objects are achieved by a forming die for shaping a workpiece, in particular a flat metal sheet, having a female part, a holding-down means and a male part, which are each arranged in a movable manner with respect to one another, wherein at least the female part, the holding-down means and/or the male part are temperature-controllable in some sections. In other words, at least one of the three elements can be provided with one or more temperature-control devices in one portion. Advantageously, the temperature-control device is fitted in the vicinity of regions of the forming die in which high degrees of forming are achieved, known as critical regions.
Furthermore, the female part, the holding-down means and/or the male part can have in some sections at least one shaping insert which is temperature-controllable. The temperature-control unit can as a result also be provided in individual segments or in individual elements of the forming die or forming die halves.
Moreover, for temperature control, at least one depression, in particular a blind hole, can be provided, through which a medium is flushable. Such depressions, for example blind holes, can be introduced into the forming die particularly easily. This can take place both during the new production of the die and subsequently during reworking or optimization of an existing forming die. The flushing of the depression with a medium affords the advantage that, by regulation or control of the supply temperature of the medium, the temperature of the die is continuously settable in the critical region of the die.
In addition, a baffle can be introduced into the depression in order to guide the medium. As a result, a flow duct in which the medium can flow along the baffle from an inlet to the die-side inner end of the blind hole, can be realized easily. At this inner end of the blind hole, the medium is deflected and guided along the baffle again to an outlet.
In addition, the surface of the die can be provided in the depression with a sealant. This affords advantages in particular when the die is formed from a porous material, for example a cast material. Since cast materials are permeable, the coolant can pass into the material of the die. In order to prevent this, according to this embodiment, the surface of the die is sealed off with the aid of a sealant at least within the depression. For this purpose, all sealants with which casting pores are able to be closed off are suitable, for example cooler sealants, waterglass, etc. Such sealants are admixed to the coolant and passed through the flow duct or the cooling system before the die is put into operation. As a result, the pores of the cast material, which are located on the surface of the die in the region of the depression, are closed off in a particularly easy and practical manner. Alternatively, for the purpose of sealing off, the surface of the depression can be provided with a coat of paint, a casting resin or adhesive. Furthermore, the surface can also be sealed off by tinning with soft solder.
Further, the baffle can be arranged in an insert, for example a sleeve, such that the medium is guided between the baffle and the inner wall of the sleeve. The use of a sleeve affords advantages in particular when the forming die is formed from a material which is not impermeable. For example, when the forming die consists of cast material such as gray cast iron, the sleeve produces a vessel which is impermeable with regard to the medium and in which the medium can be guided.
Further, the outer wall of the sleeve can be in touching contact with the inner wall of the depression. The larger the contact area is, for example by the creation of fitting accuracy between the outer wall of the sleeve and the inner wall of the depression in the die, the better the heat transfer from the medium via the sleeve into the die and vice versa. In other words, the better the fitting accuracy between the sleeve and die, the better the thermal transfer or dissipation of heat from the die into the medium. A tight fit has proved particularly expedient here. Tight fits within the meaning of the invention are clearance fits with little clearance, wherein fitting or removal is possible without tools, i.e. by hand.
For a further improvement in the heat transfer, the sleeve can be formed from a material with high thermal conductivity. Copper or similar materials are suitable in particular as such a material.
Alternatively or in addition, the outer wall of the sleeve can be provided with a heat-conducting means, in particular a heat-conducting coating or a heat-conducting paste. Further, a method for arranging a temperature-control device on a forming die for shaping a workpiece, in particular a flat metal sheet, having a female part, a holding-down means and a male part, includes the acts of identifying a critical region of the die with a high degree of forming, determining the position for the arrangement of the temperature-control device in the female part, the male part and/or the holding-down means, producing at least one depression at the predetermined position in the female part, the male part and/or the holding-down means, introducing a baffle into the depression, wherein an inlet for introducing a medium into the depression and an outlet for discharging the medium from the depression are provided, and connecting the inlet and outlet to a cooling unit.
With this method, a temperature-control unit can be provided easily and cost-effectively in or on a forming die. This method is suitable particularly for the subsequent installation of a temperature-control unit in a forming die.
Furthermore, an insert, for example a sleeve, can be introduced into the depression. As already mentioned at the beginning, the sleeve affords the advantage that cooling can be realized even in forming dies which are formed from a porous material through which the medium can flow.
Further, after the depression has been produced, the surface of the die can be provided in the depression with a sealant. To this end, a sealant is introduced into the depression, the sealant closing off the pores of the material of which the die consists. Such sealants are admixed to the coolant and passed through the flow duct or the cooling system before the die is put into operation. As a result, the pores of the cast material, which are located on the surface of the die in the region of the depression, are closed off in a particularly easy and practical manner. Alternatively, for the purpose of sealing off, the surface of the depression can be provided with a coat of paint, a casting resin or adhesive. Furthermore, the surface can also be sealed off by tinning with soft solder. As a result of the die material being sealed off, it is possible to dispense with the use of a sleeve. Thus, as a result of the number of components being reduced, the method is streamlined.
Suitable media for the temperature-control or cooling of the forming die are gaseous or liquid media, for example water, oils or emulsions. Water, optionally provided with an antifreeze, is also suitable, for example, for use as the medium or as the coolant. As a result, the medium can be temperature-controlled to temperatures below 0° C.
The embodiments of the invention are explained in more detail in the following text by way of the description of the figures. The claims, the figures and the description contain a multiplicity of features which are explained in the following text in connection with embodiments of the present invention that are described by way of example. A person skilled in the art will also consider these features individually and in other combinations in order to form further embodiments which are adapted to corresponding applications of the invention. Other objects, advantages and novel features of the embodiments of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.